COVER-SLIP PREPARATIONS. 143 



To stain the fixed cover-slip preparation it is taken 

 by one of its edges between the forceps, and a few 

 drops of a watery solution of fuchsin, gentian-violet, or 

 methylene-blue are placed upon the film and allowed to 

 remain there twenty to thirty seconds. The slip is then 

 carefully rinsed in water, and without drying is placed 

 bacteria down upon a slide; the excess of water is taken 

 up by covering it with blotting-paper and gently press- 

 ing upon it, and the preparation is ready for examina- 

 tion. 



Another plan that is sometimes used is to bring the 

 slip upon the slide, bacteria down, without rinsing off 

 the staining-fluid; the excess of fluid is removed with 

 blotting-paper and the preparation is ready for exam- 

 ination with the microscope. This method is satisfac- 

 tory and time-saving, but must always be practised with 

 care. The staining-fluid should always be carefully 

 filtered before using, to rid it of insoluble particles 

 which might be taken for bacteria. If upon examina- 

 tion the preparation proves to be of particular interest, 

 so that it is desirable to preserve it, then it is to be 

 mounted permanently. The drop of immersion oil is 

 to be removed from the surface of the slip with blot- 

 ting-paper, and the slip loosened, or rather floated, from 

 the slide by allowing water to flow around its edges. 

 It is then taken up with the forceps, carefully deprived 

 of the water adhering to it by means of blotting-paper 

 and then allowed to dry. When dry it is mounted in 

 xylol-Canada-balsam by placing a small drop of the 

 balsam upon the surface of the film, and then inverting 

 the slip upon a clean glass slide. It is sometimes de- 

 sirable to have the balsam harden quickly, and a method 

 that is commonly employed to induce this is as follows: 



